The Curious Case of a frequently discharging car battery


Read 1st Part of the Series

That Monday Morning when we received the call from the customer “The Car Battery is dead and it is not starting”, the team was as clueless as the customer was, what might be the issue??

The customer had been facing the car battery problem since the last so many months that he had purchased a pair of jumping cables which he could use to jump start the vehicle in case of no help around. The vehicle was jump started and it was brought back to the service station. The investigation started.

It was clear that there was significant discharge of current in idle state which was resulting in a full battery discharge over the weekend. But when we did our testing, we did not see any significant residual currents. To understand the scenario better, we wanted to re-create the entire scenario and test the battery.

We opened the car to open the bonnet. The car was kept idle and the battery was tested. No Residual Currents. This was puzzling. While we knew that there was significant leakage, but when we re-create the same condition nothing happens. Is it really that the car was having Monday Morning Blues!!

We were missing something.

Did we recreate the scenario completely? Yes, the car was still. It was not started. But is this the true replication of the exact scenario? Not really!!

We reached out to the customer to understand what happens with the car over the weekend. The customer responded “My daughter never uses the car on the weekend. It stays there in the underground parking”

So when the car is left with every door, window pane closed there should be a significant discharge from car battery. When we try to re-create the scenario for our ease we leave the car keys in ignition hole. The door or drive side window pane is left open for easy access to the technicians.

To re-create the exact same scenario. The car bonnet was left opened for testing current, but the entire car was locked and closed. Now this is exactly what happens (other than the bonnet is also closed in real scenario). As we measure current and voltage levels everything is fine. No massive discharge from car battery, but we continue to stick around for some more time. About 5 minutes later, we see a big spike in discharge current.

Aha!! There we see discharging current. So alas we reach closer to the discharging car battery problem. No Monday Morning Blues!! Just plain engineering at play.

But many questions popping up our heads:
1. Why a spike in current from car battery after 5 minutes of car being in locked down condition?
2. Why we did not see any discharge when either door or window was left opened?
3. If there is a short in car wiring. If so, it is there always. Why should it get activated 5 minutes after lock down?

Man! We are menial souls, why so tough problems. Inspecting the car wiring is extremely cumbersome task and we undertake the same and inspect each and every wiring in the car meticulously over the next 3 hours, but all things look fine. Our brains seems to have left us wanting.

As we fail to put the pieces of the puzzle together, we accidentally try to open the locked car from the door and the central locking system starts shouting out loudly. We need peace and no more noises. Our heads have so many unanswered questions and don’t have space for anything more. Suddenly one of the advisor’s get an idea.

“Can this be due to central locking? It is the only thing which becomes active when the car is completely locked down”

We un-assemble the main console of the central locking system and then test for residual discharges. 15 minutes of measuring currents and no residual current while we saw a spike in current levels in 5 minutes earlier.

“So this mean that the central locking console when gets activated to the safety mode after 5 minutes of lock down has developed some earthing which is resulting in massive discharge”

At last something logical which makes perfect sense. We advise the customer to use the car for a few weeks without the central locking to see if the Monday Morning Blues!! Issue persists. Three weeks later, we contact the customer and there has been no battery discharges since then. We ask the customer to purchase a new central locking and connect them with the right people. The new central locking has been replaced and it has been over 3 months since the issue haunted the customer.

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